Follicle-like structures formed by mouse embryonic stem cells (ESCs) in vitro consist of a single oocyte-like cell, which can grow as large as 70 μm in diameter, surrounded by one or more layers of tightly-adherent somatic cells. Analogous to what is observed during normal follicle formation within the ovary, somatic cells within ESC-derived follicle-like structures are connected via intercellular bridges with their enclosed germ cells, which may serve to facilitate cell-to-cell interaction required for normal follicle development.